During recovery of oil from oil reservoirs, typically only a minor portion of the original oil in the oil-bearing strata is recovered by primary recovery methods which use only the natural forces present in an oil reservoir. To improve oil recovery, a variety of supplemental recovery techniques such as water flooding, which involves injection of water through well bores into the oil reservoir, have been used. As water moves into the reservoir from an injection well and moves through the reservoir strata, it displaces oil to one or more production wells where the oil is recovered. One problem commonly encountered with water flooding operations is poor sweep efficiency of injection water. Poor sweep efficiency occurs when water preferentially channels through highly permeable zones of the oil reservoir as it travels from the injection well(s) to the production well(s), thus bypassing less permeable oil-bearing strata. Oil in the less permeable zones is thus not recovered. Poor sweep efficiency may also be due to differences in the mobility of the water versus that of the oil.
Microorganisms have been used to enhance oil recovery from subterranean formations using various processes which may improve sweep efficiency and/or oil release. For example, viable microorganisms may be injected into an oil reservoir where they may grow and adhere to the surfaces of pores and channels in the rock or sand matrices in the permeable zones to reduce water channeling, and thereby target injection water flow towards less permeable oil-bearing strata. Processes for promoting growth of indigenous microbes by injecting nutrient solutions into subterranean formations are disclosed in U.S. Pat. No. 4,558,739 and U.S. Pat. No. 5,083,611. Injection of microorganisms isolated from oil recovery sites into subterranean formations along with nutrient solutions has been disclosed, including for Pseudomonas putida and Klebsiella pneumoniae (U.S. Pat. No. 4,800,959), for a Bacillus strain or Pseudomonas strain I-2 (ATCC 30304) isolated from tap water (U.S. Pat. No. 4,558,739), and for Pseudomonas putida, Pseudomonas aeruginosa, Corynebacterium lepus, Mycobacterium rhodochrous, and Mycobacterium vaccae (U.S. Pat. No. 5,163,510). Injection of isolated microorganisms and a surfactant is disclosed in U.S. Pat. No. 5,174,378.
Additional useful microbial strains and methods for enhancing oil recovery are needed to further improve the recovery of oil from oil reservoirs.